Motor vehicle collisions are a common occurrence in today's highly mobile society. Motor vehicle designers and manufacturers go to great lengths to protect the vehicle occupants from injury by providing vehicle structures having good strength and energy absorption characteristics. It is also a goal of designers to fabricate motor vehicle structures which can withstand low-speed impacts without requiring substantial repairs. Although motor vehicle designers and manufacturers have succeeded in providing high-strength, energy-absorbing structural components, the restoration of these desirable attributes to a motor vehicle which has been damaged in a collision is of considerable concern to after-market vehicle repair facilities.
Particularly in the case of metal structural components, the deformation of a structural member during a collision produces a number of unwanted effects in terms of both the relative geometry or shape of the part and with respect to the strength of the metal. It is a goal of the repair facility to restore to the extent possible the original shape of the damaged part so that it can once again carry out its function in the vehicle. It is a further goal, however, of the repair facility to restore the original strength and energy absorption characteristics to the damaged part. While considerable attention has been paid to the restoration of shape in collision damage repair, resulting in numerous metal repair procedures and devices such as frame-straightening machines and the like, the viability of reinforcement techniques in collision repair are less developed. It will be appreciated that the feasibility of reinforcement devices and procedures is determined by a number of factors that go beyond merely restoring strength to the damaged part.
When a metal part is plastically deformed, the internal structure of the metal is changed. Thus, this type of deformation changes the properties of the metal. The original deformation of the metal structure during a collision as well as its restoration by metal repair straightening operations can be considered work-hardening. Work-hardening processes may cause brittleness of the work section due to strain-hardening and generally change the strength and energy absorption properties of the part. In many instances, for example, where frame damage has occurred resulting in a crumpled, bent or collapsed frame member, a new section of frame rail must be spliced into place. The new rail piece is commonly welded in place using arc or mig welding techniques. In order to reinforce the weld joints or to compensate for the altered compositional characteristics of a section of metal produced by cold-working, a metal plate is typically welded into the rail over the joint or worked region. This has been the traditional approach to reinforcing metal structures, and it has numerous drawbacks.
A metal plate must be cut to conform to the shape of the part to be repaired. It will be appreciated by those skilled in the art that in many motor vehicles, the vehicle frame comprises a pair of U-shaped pressings or stampings which are welded together by means of a horizontal longitudinal joint or seam and that each U-shaped pressing defines a channel. Although metal reinforcement plates are at times welded directly to the outside of the hollow rail beam, more often the spot welds connecting the two U-shaped pressings are bored out, and the more damaged stamping is removed to be replaced with a new piece. Having access to the rail channel, the reinforcement plate is usually welded to the rail within this channel. Hence, the plate must be precisely cut to fit within this designated area. Once the plate has been prepared, it must then be welded in place. There is no assurance that sufficient spot welds will be made to provide a good bond between the reinforcement plate and the rail. Moreover, the welding procedure is time-consuming and requires the additional skill of arc or mig welding on the part of the repair person. As will be appreciated by those skilled in the art, the welds promote corrosion of the metal parts and thus lead to a reduction in the integrity and life of the repaired members. A closure plate is then typically welded to the flanges of the stamping for further reinforcement which, with the channel, forms a closed space or cavity in which the metal reinforcement plate is housed.
In addition to these drawbacks, this prior art technique may change the dynamic performance of the reinforced structure during a subsequent collision. While, as stated, one goal of the repair procedure is to restore the strengthen and energy absorption characteristics of the structural member, the insertion of a metal plate in the rail may in fact reduce the energy absorption of the member or change the frame failure mode. This may result in the exertion of forces on vehicle components which were not designed to withstand these forces. Moreover, the repair procedure may not restore the original strength characteristics of the reinforced part. These factors may lead to catastrophic consequences during a subsequent collision.
In order to provide a method and device which compensates for these deficiencies of prior art repair methods, the environment in which these repairs are made must be carefully considered. While metal repair should be performed by skilled metal workers, it is often the case that many repair tasks are delegated to poorly trained personnel in neighborhood "bump shops." A lack of care in implementing any repair procedure can undermine the efficacy of the repair. Thus, a practical repair procedure must be simple to carry out and should reduce the discretion that is exercised by the repair person. Therefore, it is an object of the present invention to provide a system for reinforcing a structural member which is both simple and reliable.
It is a further object that such a system restore to the extent possible the original strength and energy absorption characteristics to a damaged structural member. It is still a further object of the present invention to provide a structural reinforcement which is both lightweight and strong. The present invention provides a process which achieves these goals by forming a reactive dough that expands in place in a hollow structural member to provide a solid, lightweight structural reinforcement.